High-frequency tube structure



y 29, 1952 D. SNOW ElAL 2,605,443

HIGH-FREQUENCY TUBE STRUCTURE Filed March 14, 1947 5 Sheets-Sheet 1 l I 2 I) I6 s I6 I I FIG. 3

INVENTORS D. L. SNOW E L GINZTON ATTORNEY July 29, 1952 D. L. SNOW EI'AL 2,605,443

HIGH-FREQUENCY TUBE STRUCTURE Filed March 14, 1947 3 Sheets-Sheet s FIG.9

FIG. |o

INVENTORS: D. L. SNOW E.L.Gl NZTON' D.R. HAMILTON Patented July 29, 1952 UNITE-D STATES PATENT DFFKIE HIGH-FREQUENCY TUBE STRUCTURE Application March 14, 1947, Serial No. 734,690

This invention relates, generally, to ultra-highfrequency electron beam velocity-modulating devices and, more specifically, to improvements in the type of single-resonator ultra-high-frequency reflex tube disclosed in Fig. 2 of U. S. Patent No. 2,250,511 for Oscillator Stabilization System, issued July 29, 1941 in the names of Russell H. Varian and William W Hansen. The present application is a continuation in part of application Serial No. 447,536 filed June 18, 1942 and which issued October 21, 1947 as U. S. Patent No. 2,429,243.

At very high frequencies, the component parts of such electron beam tubes become very small. For example, the resonator must be of such a size that resonator walls of suitable thickness are comparable in dimension to the depth of the resonator. Other problems, such as closeness of entrance and exit grid spacings, make simplicity of design necessary. When such devices are used as local oscillators, as in aircraft receivers, low electron-beam-accelerating voltages are used, resulting in low power output. Thus, elimination of either the entrance or exit grid becomes desirable as these grids stop electrons of the beam and thus cause a further reduction in power. I

Th'e'conventional reflex electron beam'velocit 12 Claims. (Cl. 315-) modulating tube contains a cathode, an entrance grid, an exit grid, and a reflector plate. The present invention provides novel means for eliminating eitherthe entrance or the exit grid.

It is therefore an object of the present invention to provide a novel electron beam velocitymodulating ultra -high-frequency oscillator, also adaptable'for use with or as a mixer, in which the exit grid is eliminated.

Another object lies in the provision of such a device in which the reflector electrode is placed in the position formerly occupied by the exit grid.

A further object is to provide filter means to prevent the escape of ultra-high-frequency energy past the reflector plate, which must necessarily be insulated from the resonator body itself.

Another object lies in the provision of velocity modulating devices, compactly designed and with a minimum number of grids, so that active electrons are not removed from the beam and fewer secondary electrons are formed.

Astill furtherobject is to provide arrangements whereby the electrons traverse different paths on entering and leaving the resonator. V Stillanother object is to provide means outside the resonator for absorbing spentelectrons of'the electron beam; 4 I

Other'objects and advantages will become apparent from the specification, taken in connection with the accompanying drawings wherein the invention is embodied in concrete form.

In the drawings,

Fig. 1 is an elevation cross-section view of a form of tube claimed in Patent 2,429,243 which eliminates the resonator exit grid.

Fig. 2 is an explanatory graph.

Fig. 3 is a fragmentary cross-section view of a modifiedportion of Fig. 1 showing means for concentrating the electron beam.

Fig. 4 is a fragmentary cross-section view of a modified portion of Fig. 1 showing electron absorption means.

Fig. 5 is a cross-section view of'an alternate form of a portion of Fig. 1 showing novel coupling means.

Fig. 6 is an elevation cross-section view of an alternate form of Fig. 1.

Fig. '7 is a fragmentary cross-section view of a modified portionof Fig. 6.

Fig. 8 is an elevation cross-section view of a form of the invention which eliminates the resonator entrance grid.

Fig. 9 shows a form of the invention which is a partial cross-section view of a modified form of Fig. 1 that has means exterior to the resonator for absorbing spent electrons.

Fig. 10 is a further modified form of Fig. 1.

Similar characters of reference are used in all of the above figures to indicate corresponding parts.

Referring now to Fig. 1, there isseen an elevation cross-section view of an embodiment of; the present invention especially useful at very-short wavelengths. A cathode emitter surface Lis supported in a focusing cylinder 4 on which is mounted a mesh wire grid 3 directly in front of emitter I, both cylinder 4 and the hot cathode being supported from insulator 5.-. Lead wires 2 feed current to a heater coil (not shown) inside of cathode I. Voltages are applied to leads 2 and to focusing shield 4 by means of leads 6, 1 respectively, which pass through the glass portion 3 of the vacuum envelope. The cathode structure is centrally positioned in a cylindrically apertured conducting member 9, which also supports resonator entrance grid I0 parallel to cathode emitter surface I. Grid [0 may consist of alternate short and long conducting radial vgrid wires. Member 9, together with flexible conducting diaphragm I2 mounted thereon, forms one wall of a cavity resonator, the remainder of the resonator being enclosed by resonator body I i.

As shown in Fig. 2 of the aforementioned U. S.

Patent No. 2,250,511, there is usually provided opposite the entrance grid II] and positioned centrally in resonator body II, a second or exit grid similar to grid I0, through which the electrons from cathode I pass. After the electron beam leaves the resonator it is reflected back thereto by means of a reflector electrode operating at or near the potential of the cathode. If an ultrahigh-frequency electromagnetic field exists within the resonator, the electron beam undergoes recurrent velocity changes by the action of the field during the beams initial passage through the resonator. As the electron beam passes beyond the resonator toward the reflector 'elec: trode, the effect of the velocity mgxiulation is to commence recurrent grouping of the electron beam. The spacing between the resonator exit grid and the reflector electrode, and the voltage on said electrode are so arranged that the electrons are reflected back into the resonator at a time when the velocity modulation has resulted in density modulation producing electron groups and the electron groups return energy to the elec tromagnetic field thereby maintaining it. Direct current, introduced into the device by means of the electron beam, is thus converted into ultrahigh-frequency energy and may be removed from the resonator by means of coupling loops and associated concentric line elements.

In the present embodiment of the invention, however, the exit grid is dispensed with, and the reflector plate is introduced in a novel and useful manner. As seen in Fig. l, the reflector surface I8 is positioned substantially flush with the inner conducting surface of resonator body II. The surface I8 is the flat end surface of a quarter-wave long cylinder I9, which forms a portion of the first section of a low-pass filter consisting of an outer cylindrical conducting tube I'I surrounding concentrically an inner conducting member comprising approximately quarter-Wave long sections I9, 20, 2I, 22 which are alternately large and small in diameter, The last small diameter section 22 of the filter protrudes through glass-to-metal seal 23, thus providing support for the inner conductor of the.

filter. The filter is provided in order that a voltage equal to the cathode voltage, or some other desirable voltage may be supplied to reflector surface IS without the loss of ultra-highfrequency energy from the oscillating electromagnetic field inside the resonator. Any number 'of filter sections may be employed; however, four alternately large and small diameter sections ordinarily provide adequate attenuation. The design and operation of such filters have been described in copending' application Serial N 0. 417,229, entitled High Frequency Tube Structure, filed October 31, 1941 in the name of William W. Hansen, now Patent No. 2,506,590.

Energy may be removed from the resonator by coupling loop 24, which is shown at the termination of coaxial line 25. In very short wave devices of this type, the resonators may be so small that coaxial lines of conventional size cannot conveniently be utilized; consequently line 25 is made very small in diameter. Both conductors are expanded in tapered section 25 to adapt the line to a section 2 of normal size. Continuity of the vacuum envelope is provided in line 21 by the glass-to-metal seal 28. Tubular outer conductor 29, with its threaded flanged portion I4, serves in the conventional manner as a connector'to a conventional coaxial line to 4 lead energy to utilization apparatus. Additional coupling loops mayv be supplied, if desired.

A spider, fixed on reentrant member 9 and having three legs I3 spaced opposite three legs I5 attached to resonator body II, forms, together with screws I6, means for tuning the resonator by variation of the space between grid I0 and reflector I8, in thewellknown manner. Other Well known tuning devices, as shown in later figures, may be used if desired.

One mode of operation of the device may be described with reference to Fig. 2, illustrating an idealized graph of space potential as a function of distance between the cathode I and the reflecting surface, I8. The reflector is assumed to-be at cathode potential, and the effects of space charge are neglected. As seen in Fig. 2, the potential on any electron in the space between cathode I and reflector surface I8 is an increasing function of the distance from cathode I. After passing through grid IB, the electron is acted upon by a field which is the sum of a constantly decreasingpotential and the alternating potential due to the ultra-high-frequency oscillating field between grid Ill. and reflector I8. Dotted lines 48, 48 represent extreme conditions of this resultant field. Electrons, accelerated by the direct voltage between emitter I and grid I0, pass through grid 10 with a uniform velocity, andv while traversing the space from grid Ill to their point of reflection and back through the grid I0, are velocity modulated in the conventional manner. After passing through grid ID. in the reverse direction, the electrons are reflected in front of the cathode structure and are again directed through grid Ill. During this last reflection, the electron beam has become density-modulated, and returns to the space between grid II] and. reflector I8 to give up energy to the oscillating electric field therebetween, thus maintaining electromagnetic oscillations in the resonator. It is seen that the distance between grid I0 and the point of reversal of the paths of the electrons in front of reflector I8 and cathode I isv determined by the flight time necessary to bring the density modulated beam into the oscillating electric field at the proper instant to give up energy to that field.

Analysis of another mode; of operation of the device shown in Fig. 1 may also be made similar to, the analysis ofoperation of the electron beam velocity modulating reflex: devices disclosed in the above mentioned U. S, Patent No. 2,250,511. Electrons from emitter I are focused into a slightly converging circular cross section beam by f0- cusing shield t, and have been accelerated by the cathode voltage on reaching entrance grid I0. In traveling from grid II! toward reflector surface I8, the beam is velocity modulated. With proper interelectrode spacings, and with the proper reflector voltageall of the electrons are reflected before reaching surface I8 and travel again toward grid I0. During the interval of reflection, the velocity modulation of the elec-. tron beam has resulted in density modulation, in such a manner that these electrons give up energy to the oscillating field thus maintaining it. It is again seen that interelectrode distances are determined by the necessary electron transit ime.

If the voltage impressed on reflector surface I8 is not sufficient to reflect those electrons which are most accelerated during the velocity modulation process, they will be. collected. by the reflector. Surface ;|8..mayT be. provided under such. circumstances: with a; secondary electron suppressing..materia1.: The .action may; be spokenofraselectron 'beam density modulation by Electronsentering theresonator one-half cycle later findi the oscillating field opposing their motion, and'thus. supply energy to the field These electrons are .sodecelerated by the retard-- ingpotential ofreflector l8 that they are reversed in directionwithout striking the reflector. As the reflected electrons travel back toward grid 10, the oscillating field has again reversed; consequently the electrons again add energyto the field.' The result 'is'ia positive addition of energy to the oscillating electromagnetic field, so that the field is maintained. The device of Fig. 1, as well as alternate forms to be further discussedin connection with later figures may thus operate as 'simplevelocity modulation device, or as an absorption density modulation device, as desired. I I

Fig. 3 illustrates a slight modification in the configuration ofthe electrodes of the device of Fig. 1. The cathodeand heat or focusing shield 4 are seen to be similar to those of Fig. l. The radial grids ll] of Fig. 1 are, however, replaced by ak'nitted or woven grid 30, which is preferably made of a conducting material or may be plated with a conducting material. The'grid 30 is made to bow away from the focusing shield 4 into the resonator space. The first section I9 of the filter is modified so that its upper reflecting surface. I8 is concave. The surface l8'.may be parallel to the surface 30 or may not, as desired.; The actual configuration is empirically adjusted to give ,best focusing of the electron beam, and it seems evident that one skilled in the art may use many modifications of the grid and reflector plate shapes shownin Figs. 1 and 3..

If the device of Fig. l is operated by the absorption bunching principle, I the modification shown in Fig. 4 isuseful. In this figure the first section IQ" of the filter is modified so that the reflecting surface I8 of Fig. 1 isv replaced by a grid 33 which may be a woven or knitted grid. The cylinder I9 is made hollow and contains in its bottom a reentrant conical projection 34. In operation,,the electrons which pass the grid Ii] at a time when the oscillating field in the resonator accelerates them,.pass through the grid 33 and are collected by the Faraday cage action of theelement IS". The cone 34 is provided so that secondary electrons emitted when high energy electrons strike its surface will not be reflected back into the resonator cavity. Alternatively, if desired, the surface [8 of the reflector may be coated with a secondary emission substance, 'so that density modulation is caused when high speed velocity modulated electrons strike the sur-' face [8. It will be clear that the reflecting elec trode of any of the modifications to be described may be similarly coated.

With reference to Fig. 1 it was stated that for very small wavelength devices of this type it may sometimes be diflicult to introduce coupling loop 24 and its associated coaxial line. Fig.5 shows a. modification of the structure of Fig. 1 combining the energy-removing device and the filter through which the reflector voltage is introduced. Only section I 9 of itheffilter' is used, concentrically supported in anputer conducting tube'35 by an inner conducting rod 46. Rod 46 is inturn supported by a rod36 which passes out through a glass-tometal seal 38 in the end of. tube 35. At the junc-' tion betweenlrods Hand 46, rod 36 has a small diameter projection 47 which is a quarter wave long andzwhich is inserted into acentral hole in rod 46,. rods 36*and 46 .being'insulated fromeach other. by means. of aninsulating bushing 48 -ap proximately. a quarter wave long. Attached at right angles to rod 46 .is. a small diameter innerconductorMl-which passes through a hole in outer tube 35;? Outside of. tube .35, conductor 40 is .con-

centrically surrounding by a conducting tube 39.

Near. the" outer end of..tub'e 39 the inner conductor40 is expanded .into a section 43 almost'equal the. inner. diameter of the tube .39 and insulated therefrom .by an insulating bushing 44. Section 43 of the line. is lmade approximately a quarter wave long-and i's terminatedby a lead 45. A glass-toJ-metal. seal 42 is provided to giveqcontinuity totheivacuum'envelope; l 1 Y Inithe operation of Fig. 5, a .voltage equal to or near cathode voltage isapplied to the lead '45 and is thus directly introduced to the reflector plate surface 18. The filter section l9 allows an arbitrarily chosen amount of energy to flow down the concentric line 46; 35 and may be designed so that a maximum amount of. ultra-high-frequency energy can be removedfrom the resonator without overloading it and causing oscillations to stop. The insulating section'48 prevents the reflector voltagev from going outlon the inner conductor36 :to utilizationapparatus, and the filter section 43 prevents ultra-high-frequency from leakingout into space, the coaxial line 39, 40 being designed to have very high impedanceat the frequency, used. Thetube 35 isgprovided with a threaded flanged portion3l, to which a conventional coaxial cable may be attached. Filter section l9 may be a hollowFaraday cage similar to section I 9""of Fig. 4, if desired.

Referring nowto Fig. 6, there isillustrated a modification of the device of Fig. 1. in which thermal tuning of the resonator is readily accomtended to providethe outer conductorof a coaxial filter whoselinneri conductor comprises alternately large and small portions 58, 59, 60, and 6!. A centrally apertured conducting plate 63 .closes the tube '51 and terminates the filter. The

last'small diameterfportion 6! of the. filter consists of a thin walled conducting tube which has an extension 65 projecting. through the aperture in-the plate 63. Extension 65 is concentrically surrounded by a tube 64 attached to the plate 63. A glass seal 66 between tubes 64 and 65 provides continuity to the vacuum envelope as well asan insulating support for the inner filter structure.

This construction allows the surface 53 to be.

maintained at a desired potential with respect to the entrance grid III while preventing radiation loss from the resonator 55 through the glass seal 66. Tube extension 65 contains a cartridge or other type of heaterBZ to which power is applied by leads 68 passing througlr an insulator Bl.

Power applied to the heater 62 causes expansion of the thin walled tube 6I,"65; consequently the spacing between the entrance grid l0 and there fleeting surface"53 is alteredby the motion trans .mitted -downthe entire-irmer' conductor of the filter. .g'Ihus ;the .resonant=frequency of the resonatorii-may be yaried at will inthe well known manner Itv will .be lclearthat similar tuning means may be applied toany -.of zthemodiflcations described in the present specification.

Electrical tuning may bereadilyeflected in'the device of Fig.6 bysvariation of the voltageapplied to the reflector electrode .53. As is well known in the art, such a tuning method is most .useful with low .Q,,.high shunt. .impedance resonators. Ifthe protruding portion 54 and .the electron beam are made very small .diameter as compared .to the diameter of the resonator, a low Q resonator results: If: desired, these features may be combined in the device of Fig. .6, electrical tuningbeing used :toprovide changes over small frequency ranges,'.and thermal tuning'being employed to :provide'changesover large ranges. If desired, the protruding portion 540i the resonator 55;may beomitted, as seen in Fig. 7. In this case resonator 55' has a very high Q and has a considerably lower eifective shuntimpedance than the resonator 55 of 6. 7

Referring now .to Fig. 8 there is illustrated a form .of theinvention in which the entrance grid to the resonator is omitted, an exit grid being supplied-. An emitter surface BI of a cathode 80 is placed coincident with the usual position of the entrance grid and a filter :isprovided around the cathode 80. :Thecathode 80 has along tubular heat shield :mounted on insulating washer 82 and is: suppliedzwith heating power by leads 83 connectingto leads/86 which pass out of the vacuumenvelope throughglass-to-metal seals 81. Concentrically-surrounding the cathode tube 80 are small and large diameter conducting cylindrical tube sections 89; 90, 9I, 92 and 93 respecnegative potentiaL- The last portion 93 of the filter is fastened to an annularplate 98 which comprises, together-with cylindrical tube I03 and focusing shieldiI32 having at :its outer .end a focusing grid' I.3.I which .is substantially parallel to the emittingtsurface of cathode I130. .An entrancelgridI3'I to La resonator 138 is made .substantially conical, the cone pointing toward the center of'the grid l3I. The exit grid of the resonator is again omitted, the reflecting voltage beingapplied through a filter I43 to a conical protruding reflector Hi5 whose convex surface may :be .parallel :to that .of grid I31. Electrons from which energy has been extracted are now reflected toward agrounded annular plate I33 surrounding .the focusing grid I'3I., :so that substantially :none :of these electrons are allowed to strike the emitting surface of the cathode. Also, in this .form .of the invention, the incident electrons travel difierent paths from the reflected electrons, .:so that difficultiesdue to electron dispersion, and to the possibility of a further entry of the reflected 'electronsfinto the resonator are avoided.

Fig.1!) shows aslightimodiflcation of the device of ;Fig.-9xwhichis useful for a similar purpose. .A cathode I110 is;mount.e d with its axis of symmetry at an angle with theaxis of symmetry of a ;reso-' through the grid I11 and are collec ed by conopposed apertured plate IOI,the resonator I00."

A cylindrical tube I I0 supporting an exit grid I02 projects through the aperture in" plate IOI. A conventional[reflecting electrode I 08'. mounted in the proximity of, the grid I02 by a glass seal I I I which both provides continuity to the vacuum envelope and electrical insulation for the conductor I09. Tuning of the resonator I00 is shown to be accomplished by a conducting or dielectric plug I I3, which, by rotation of knob II5, may be insertedto a, greater or lesser degree into the resonator. Reentrant glass tube I I4 surrounding the plug I I3 is sealed to a concentric metal tube II2 inserted in the side I03 of the resonator to provide continuity of the vacuum envelope. The operation of such a tuning device is to cause distortion of the electromagnetic field inside of the resonator, thus altering its natural frequency in a well known manner. v r g V Fig. 9 shows a form of the present invention most useful when operated as a simple electron eam refle ve o it -modu ating devi e; A catha'il! is seenmounte aa pncentrictubular on a conductor I09 is held within the tube H0 ducting wall I15. It seems apparent that any desired. method of tuning of the resonators of Figs. 9 and 10 may be used.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. High frequency apparatus comprising a cavity resonator having an entrance means through which an electron beam is adapted to pass, said resonator having exit means, a reflector electrode positioned adjacent said resonator exit means and insulated therefrom, said reflector electrode havinga convex surface opposing the eiectron beam, means for projecting the electron beam into said resonator through Said entrance means and toward the convex surface of saidreflector, and means for applying a potential difference between said reflector and said resonator to cause said beam to be reflected by said convex surface along a path different from that 'of the projected electrons and outwardly thereof.

2. A generator of electromagnetic waves comprising an apertured electromagnetic resonator adapted to contain an oscillating field therein, non-planar electron-permeable means bowed outwards from. the aperture of said resonator, means in said generator for producing an electron stream and for projecting the stream into said resonator through said permeable means to effect velocity modulation of the stream by the field within said resonator, means in said generator including an electrode extending into said resonator and insulated therefrom for opposing the electron stream to effect density modulation thereof between said electrode and said electron- ;permeable means, wherebysaid density-modulated stream delivers energy to the electric field to maintain the same, and means outside said resonator for absorbing the stream after delivery of energy to the field.

3. A high frequency tube structure comprising a hollow cavity resonator adapted to contain an oscillating electromagnetic field and having opposed apertured walls, a non-planar entrance grid formed in one of said walls and projecting outwardly from said resonator, and a reflecting electrode occupying an aperture in the opposed wall, said reflecting electrode having a centrallyprojecting portion, whereby electrons reflected by said electrode pursue paths different from the incoming electrons.

4. A high frequency tube structureas in claim 3 further comprising electron receiving means located outside said resonator for collecting said reflected electrons.

'5. A high frequency tube structure comprising a hollow cavity resonator adapted to contain an oscillating electromagnetic field and having opposed apertured walls, an entrance grid disposed in one of said walls and projecting outwardly from said resonator, and a reflecting electrode occupying an aperture in the opposed wall, said entrance grid and said reflector electrode having substantially parallel conical surfaces, whereby electrons reflected by said electrode pursue paths diilerent from the incoming electrons.

6. High frequency apparatus comprising a cavity resonator having an entrance means through which an electron beam is adapted to pass, said entrance means comprising a conical grid structure, a reflector electrode forming a portion of the wall of said resonator and insulated therefrom, said electrode being conical and coaxially disposed with respect to said grid, means adjacent said grid for projecting an electron beam through said entrance grid toward said reflector electrode.

7. A high frequency tube structure comprising a hollow resonator adapted to contain an oscillating electromagnetic field and having opposed apertured walls, an outwardly extending conically-shaped entrance grid occupying an aperture in one of said walls, a conically-shaped reflecting electrode occupying an aperture in the opposed wall, means adjacent said grid for projecting a beam of electrons'through said entrance grid for exciting electromagnetic oscillations within said resonator, and filter means including said reflecting electrode as an element thereof for preventing undesired radiation of the electromagnetic energy from said resonator by way of said electrode.

8. High frequency apparatus comprising a cavity resonator having an entrance means through which an electron beam is adapted to pass, a reflector electrode positioned adjacent an aperture in the wall of said resonator and insulated therefrom, means including a cathode for projecting an electron beam through said entrance means into said resonator toward said electrode, said electrode having a substantially conical portion facing said beam for reflecting the latter backwardly and outwardly of its initial path through said resonator, thereby preventing said beam from again entering the cathode region.

9. A high frequency tube structure comprising a hollow resonator adapted to contain an oscillating electromagnetic field and having an apertured wall, cathode means on one side of said wall for projecting a stream of electrons through said wall and into said resonator, and means on the other side of said wall including a reflecting electrode having a convex surface for reflecting said electrons back toward said wall and along a path different from and extending outwardly of that of the projected electrons,

10. High frequency apparatus comprising comprising means including a cathode for projecting a stream of electrons along a first path, a hollow resonator along said first path adapted to contain an oscillating electromagnetic field and having an electron-permeable grid with a central convex portion located coaxially with said cathode and extending in the direction thereof, means including a reflecting electrode for reflecting said electrons back toward said grid and along a second path outwardly of said first path, said reflecting electrode being located coaxially with said stream projecting means and further having a central convex portion extending in the direction of said cathode.

11. A velocity modulation electron discharge device comprising a cathode electrode means for producing an electron beam, means coupled to said beam including a cavity resonator for velocity modulating said beam, and a reflector electrode means having a convex surface for reversing the direction of said beam to cause said beam to retraverse said resonator along a path extending outwardly of the initial path, one of said electrode means providing part of the field boundary of said resonator.

12. Apparatus as in claim 11, further including filter means coupled to one of said electrode means for minimizing the leakage of high frequency energy from said resonator.

DONALD L. SNOW. EDWARD L. GINZTON. DONALD E. HAMILTON.

REFERENGES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,128,234 Dallenbach Aug. 20, 1938 2,128,235 Dallenbach Aug. 20, 1933 2,157,952 Dallenbach May 9, 1939 2,167,201 Dallenbach July 25, 1939 2,278,210 Morton Mar. 31, 1942 2,314,794 Linder Mar. 23, 1943 2,351,895 Allerding June 20, 1944 2,2 Litton Mar. 27, 1945 2,402,983 Brown July 2, 1946 2,406,850 Pierce Sept. 3, 1946 2,411,913 Pierce et a1 Dec. 3, 1946 

